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GM’s View on Battery Technologies for Hybrids, Plug-Ins and E-Flex

Energy and Power requirements for full hybrids (two-mode), plug-in hybrids, and E-Flex range-extended EVs. Click to enlarge.

GM held a media briefing yesterday, along with its battery partners from Johnson Controls-Saft, A123Systems, and Cobasys, to provide some perspective on the development of lithium-ion battery technology for its plug-in and E-Flex efforts.

Interest in and demand for the Chevrolet Volt, the series plug-in hybrid concept car unveiled at the Detroit auto show, has been intense and gratifying, according to the GM executives, but they also want to manage expectations as best they can around the key issue of battery development.

On the one hand, we want to be excited. On the other hand, we’re getting emails asking if [they] can buy the Volt tomorrow. It’s important to understand that a lot of work remains before the batteries are ready for mass production. It’s a balance between the promise and the hurdles that remain.

—Scott Fosgard, Director of GM Powertain and Advanced Technology Communications

Joe LoGrasso, the engineering group manager for hybrid energy storage systems at GM, noted the difference in power and energy requirements between a standard two-mode hybrid, a plug-in version of such a hybrid (the Saturn VUE two-mode plug-in under development, earlier post), and an E-Flex range-extended EV such as the Volt (a series plug-in hybrid in configuration, earlier post).

In GM’s view, all-electric mode in a conventional two-mode hybrid at this point is limited to lower speeds and loads. EV mode in a plug-in two-mode hybrid such as the Saturn VUE will support a range of 10+ miles, and the E-Flex/Volt series hybrid plug-in will provide 40+ miles all-electric range.

A plug-in version of a two-mode hybrid would require about twice the discharge power and significantly more usable energy than a conventional two-mode hybrid battery pack. In turn, a range-extended, battery-dominant plug-in series hybrid such as the Volt would require more than twice the discharge power and usable energy of the plug-in version of a two-mode, according to GM’s view of vehicle requirements.

GM’s View of Hybrid and Plug-in Hybrid Battery Requirements
Plug-in Hybrid
Range-Extended EV
EV Range Only at low speeds and loads 10+ miles all-electric in city 40+ miles all-electric in city
Recharge Only while driving While driving and with plug-in While driving and with plug-in
Power EV driving in low-speed city only EV driving in city EV driving full vehicle performance
Life 10 years
150,000 miles
10 years
150,000 miles
10 years
150,000 miles
Battery technology and vehicle requirements. Click to enlarge.

GM and its battery partners asserted that lithium-ion batteries will provide the range of solutions required to support the different vehicle applications. The chemistry offers both high energy density and power density, and as such is necessary for future hybrid performance and critical for plug-in and E-Flex applications. Ongoing developments in new materials such as lithium titanate anodes and lithium iron phosphate cathodes continue to improve performance.

Different battery requirements for the different types of cycles. Click to enlarge.

But GM also took pains to outline the challenges for battery design optimization given the different requirements between charge-sustaining and charge-depleting applications.

(In terms of areas of focus for GM in future energy storage, the company also noted that supercapacitors, because of their very high power density and potentially low cost, may be very well matched by mild hybrid applications.)

Different applications require different li-ion cell and pack characteristics. Click to enlarge.

Li-ion cells designed for a charge-sustaining hybrid application require high power but low energy, and feature ultra-thin electrodes, thicker current collectors and short pulse power.

Cells designed for plug-in and E-Flex applications require both high power and high energy, and thus thicker electrodes and thinner current collectors. The batteries must be able to support longer power draws.

While GM is working with a battery pack built from large format cells for the two-mode plug-in, and an array of two or three such large-format packs for the E-Flex. However, GM is also exploring a single battery pack made of very large-format cells for the E-Flex as well.

The key challenges to making lithium ion successful are robustness, cost and life. While today it may not be ready for prime time, it’s not a revolutionary requirement but evolutionary advance that will help us meet the requirements.

GM is using a multi-phased approach, starting with qualifying the cell, proving out the cycle life and calendar life at the cell level, then developing the pack and testing it on the lab bench. All this is necessary as a precursor to declaring a solution ready. Vehicle integration is the final step before the production program. The challenge is how do we develop battery solutions and vehicles in parallel?

—Joe LoGrasso

Mary Ann Wright, the former chief engineer for the Escape Hybrid and new CEO of JCS (earlier post), provided a brief overview of lithium-ion chemistry and cell construction, noting that manufacturers can balance the power and energy based on system requirements in part by making the lithium-ion electrode coating thicker for energy requirements and thinner for power and acceleration.

Theoretical voltage and capacity is a function of the anode and cathode material. The practical capacity brings in the effect of the separator, the electrolyte, the connector, the temperature and the rate.

—Mary Ann Wright

She also emphasized the critical success factors of useful life and reliability, and automotive-compliant quality. The automotive environment, she stressed, is much harsher than the consumer environment, especially in terms of use and abuse and thermal management.

Ed Bednarcik, vice president and general manager of the pack and system group from A123Systems, provided an overview of manufacturing processes. Producing high-power li-ion batteries requires the use of nanomaterials that need proprietary mixing, handling and coating processes and systems, he noted.

The use of very large currents (100 times grater than conventional li-ion) require new termination and current collection schemes. To prevent contamination, the electrodes are assembled in clean room environments.

The additional burden of a 10-15 year battery life (compared to a 2-3 year life for consumer applications) also requires different assembly processes to seal the cells such as the use of laser welds to provide superior hermetic packaging.

The major battery pack system components. Click to enlarge.

Scott Lindholm, the vice president of systems engineering from Cobasys, focused on the development of the battery systems, rather than the individual cells. The three major components of the battery system are the batteries, the thermal management system, and the electronics bay. An initial challenge faced is the mechanical packaging, especially in vehicles not originally designed to hold large battery packs.

Batteries like to live where we live. They like to live at the same temperature. If we can’t control the battery temperature, we lose control, and the system will fail. Things you may not consider—salt-mist testing, vibration, thermal shock, mechanical shock—are all wrapped into the system design.

From the consumer perspective, we want to ensure there is no exposure to high voltage. What happens when a kid dumps a Slurpee down the back seat?

—Scott Lindholm

The focus on the 10-15 year, 150,000-mile battery life appears iron-clad, despite suggestions from some, such as Felix Kramer of CalCars, that there might be the possibility of negotiating a lower regulatory requirement and/or supplementing that with a warranty package in favor of getting more cars into production more quickly.


Jack Rosebro

"What happens when a kid dumps a Slurpee down the back seat?"

Ask Toyota, or other hybrid manufacturers. Liquids have already made their way into battery pack compartments that are mounted underneath rear seat assemblies - as, for example, Toyota's Highlander Hybrid and Lexus RX400h, among other current hybrids. In addition to spilled drinks, over-aggressive shampooing of interiors by detail shops have also caused problems. In every case that I am aware of, the system's ground fault detection system properly identified the problem and shut down the system.

Although these cases are not common, investigation has shown that adjustments to the original case designs could have prevented some of the ingress. As with any new technology, OEMs will learn from experience. Some will learn faster than others.


The problem of specific power is entirely sidestepped with a large battery, such as you would have in a PHEV.

I note their PHEV cycle test used 80% to 20% cycling (60% of capacity). With Altair they could use 95%.


What all this clearly shows, is that the battery tech is absolutely there for all aspects of power and energy delivery is there, what needs to be done is systems integration.
Stick in a pack of ultracaps for acceleration power and regen braking, and get the energy to drive from lipo batteries, and you are home free. The rest is power electronics to manage the charge distribution.

Tesla and others have shown that its doable, for long-range EVs. GM is still dragging their feet in implementing this stuff, and there is no excuse why they are starting this just now. They shoulda kept going and rolling out better prototype iterations since EV1. Its not like lithium wasnt on the radar when EV1 were pulled off the streets.

Wishing for the better battery to suit all our needs will remain a unaccomplished dream forever ( battery-powered passenger aircraft, anyone ? ) , meanwhile others are rolling out EVs that suit the needs of certain people.


Put it in simpler terms, better is the eternal enemy of good enough, and it has been shown countless times that batteries/capacitors are good enough right now to rid us of oil dependence in our personal transportation needs, in 95% of the cases.


The reason for starting at 80% for the PHEV cycle test and not 100% probably means that the Johnson Saft battery will last longer that way. Or is there another explanation? The same argument could be true for stopping at 20% but here the reason could also be that a 20% state of charge is needed to maintain sufficient power. I would like to know how the batteries from Saft, A123 and Altair compare in this regard. Clett you seem to know this for Altair could you perhaps elaborate a little on it? Anyway it is nice to see that GM has chosen to be more informative on these PHEV development issues than they would normally be.


Kert, Tesla hasn't proved anything yet. 3 or 4 years after the cars are released we will know how durable they are. Until then its all speculation. Plus, making a full EV is easier than an PHEV by a long way. Take Tesla's pack and make it 1/5th the size, stick it in a PHEV and I bet it wouldn't last longer than 2 or 3 years.

Mark A

I agree with Pauls answer to Kert. Tesla hasnt proved anything yet. They have proved that they can build a high priced toy for the "Jay Lenos" and "George Clooneys" of the world, but not for "factory worker Joe" whose livelihood may depend a single vehicle and its performance/value.

Battery technology and durability have to improve, and I feel they are. Tesla does not have the product awareness that GM has, and would not take as big of a risk/beating with a product introduction of unproven, developing technology. So a comparison of Tesla to GM is totally senseless in this case.

As far as GM dragging their feet, I disagree, as I feel they are only going to implement these technologies after they are comparable in PRICE,RANGE, and DURABILITY with existing ICE offerings. Just the fact that they are at "the game", if not in "the game" gives me hope for our future transportation. Dont pin our hopes on Tesla, as I feel Telsa will only be a small part of the future. Hopefully I will be wrong. Either way, with the improving EV vehicles in the future our future is indeed bright. The battery gestation period is long, and we are an impatient animal.


Remember Toyota's Watanabe himself has told the world that the battery powering the next Prius, in the showrooms next year, will be lithium-ion.

I doubt Toyota would put in anything less than a 15-year pack.

Richard  Cohen

I can't wait for next years auto show when GM will offer the first car to run on cat urine. Strange isn't it, that someone would actually want to buy a car GM displayed at the show. No wonder Toyota is leaving them in the dust.


Thanks Richard for the token GM bashing comment. Geez...people criticize GM for not being green enough, then criticize them again when they are trying. No winning here.

Personally I have nothing against either Toyota or GM, they both have some nice vehicles in all categories. But I say, give GM a chance, they are trying. The future of EV transportation needs companies like GM whether you want to hear it or not.


Kert -

The main reason for not fully discharging the PHEV pack to 0% or even 5% SOC is that you still have to maintain HEV, or charge sustaining, activity at that state of charge. It is dubious that Altair would be capable of pulling the power required for any significant time (if at all) at 5% SOC.

Harvey D.

Is GM that serious about PHEVs and BEVs? It sounds more like a PR effort to stay in the front page cheaply. Can an affordable PHEV or BEV be produced by the Big-3 in USA?

My bet is that Toyota will have the first affordable mass produced PHEV on the market in late 2009 early 2010. GM will follow (with an electron guzzler?) about 2 years latter.

In the longer run, have a closer look at what China is doing. China has the requirement (not enough oil and/or alternate fuels) but can mass produce the Energy Storage Units (ESU) + electric motors + electronic control systems + light weight vehicles at a much lower cost than Japan or USA.


But could not the Altair battery cycle between 95% SOC and 15% SOC, providing an AER of 80% of the battery capacity? If a PHEV packed a 20 KWH battery, then 16 KWH would be available for an all electric range of 45 miles. These batteries are available now, the ability to connect them together is available now, and the electrical power control system is available now. The Volt could go into production now, it is not constrained by technology. Cost and production capacity are the real barriers.

Dustin in Ohio

IIRC - the Volt is supposed to get 50 mpg even after the batteries are depleted. So if GM says the batteries are the problem, then they should design a void/space to put them, and sell the car without batteries. Make them an upgrade option. Hell sell different versions/types etc... Put the infrastructure in the car - the Plug In connector etc.... but just don't install batteries.

GM would instantly have a 50mpg electric car that runs with an ICE as a generator (I'd prefer diesel), and which could be upgraded now or later with batteries to compliment the ICE.

Technology off the shelf, avoids the purported problem of batteries and immediately proves that GM is not green washing, but actually doing something for the American car consumer.

Sounds like a no brainer to me... I'd buy one today! (No joke, I have a Civic on its last legs. Really, I'd buy one today).

The ball is in GM's hands... Will they decide to make vehicles or just greenwash? The decision is likely to determine whether they will prevail/hold their own/fail against Honda and Toyota.


I'm guessing here, but I think the small engine that is in the volt concept would be too weak to power the entire vehicle alone--if that is what you are getting at? I think that motor is small due to it only needing to run a generator to produce electric for re-charging, and therefore is efficient at sipping gas rather than gulping. In a scenario as in the rest of the cars that are run directly by an ICE, any amount of speed, or hauling, or towing, or hill climbing asked of the vehicle starts to kill the fuel economy.

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